Optical radar apparatus

ABSTRACT

The invention aims to increase an expansion angle in a road surface direction in a short-distance area without setting a detection range one-sidedly and without sacrificing a maximum detection distance. 
     A double-focus lens is integrally formed by disposing a short-focus portion in the vicinity of a center and a long-focus portion on the periphery of the short-focus portion. A light source is disposed at a distance slightly shorter than the focal length of the short-focus portion of the double-focus lens. When light is emitted from the light source to the double-focus lens, light emerging from the short-focus portion has a small expansion angle such as not to diffuse largely. Therefore, the emerging light can be caused to reach a long distance. On the other hand, light emerging from the long-focus portion has a large expansion angle such as to diffuse to some extent. Therefore, the emerging light can be caused to travel over a short-distance area and, more particularly, over an area extended in a widthwise direction of a road surface.

TECHNICAL FIELD

This invention relates to an optical radar apparatus, and is used, forexample, for a constant-speed traveling apparatus and an optical radarapparatus capable of accurately detecting the position of a vehicle, anobstacle or the like moving closer to a detection-side vehicle.

BACKGROUND ART

As optical radar apparatuses capable of setting a detection area in awidthwise direction of a road surface, there are apparatuses such asthose disclosed in Japanese Utility Model Laid-Open Nos. 59-117980 and59-117981.

In the apparatus disclosed in Japanese Utility Model Laid-Open No.59-117980, shown in FIGS. 7A and 7B, light from a light source iscondensed to some extent by a lens to obtain a first detection rangeθT1, and the light source is suitably moved to obtain a second detectionrange θT2 wider than the first detection range θT1 in a widthwisedirection of a road surface by changing the degree of condensing of thelens.

In the apparatus disclosed in Japanese Utility Model Laid-Open No.59-117981, shown in FIG. 8, light from a light source traveling througha lens is diffused by a prism to increase an expansion angle in a roadsurface direction, thereby setting a detection range wide in a widthwisedirection of a road surface.

In the apparatus disclosed in Japanese Utility Model Laid-Open No.59-117980 among the above-described conventional apparatuses, shown inFIGS. 7A and 7B, however, light cannot be emitted simultaneously for thefirst detection range θT1 and the second detection range θT2, and thedetection range is set one-sidedly, since the detection range is changedby moving the light source.

The apparatus disclosed in Japanese Utility Model Laid-Open No.59-117981, shown in FIG. 8, entails the problem of a reduction in themaximum detection distance because light is uniformly diffused by theprism. Because of this problem, it is not possible to meet a demandheretofore made for widening the detection range in a widthwisedirection of a road surface in a short-distance area without reducingthe maximum detection distance when an optical radar apparatus is usedfor an inter-vehicle control or an obstacle detecting apparatus.

The present invention has been achieved in consideration of theabove-described problems, and an object of the present invention is toprovide an optical radar apparatus capable of increasing the expansionangle in a road surface direction in a short-distance range withoutsetting the detection range one-sidedly and without sacrificing themaximum detection distance.

DISCLOSURE OF INVENTION

According to the present invention, an optical radar apparatus istherefore adopted in which a beam of light is emitted from a lighttransmitter, reflected light from an object is received by a lightreceiver, and the distance to the object is detected on the basis of alight transmitting-receiving relationship, the light transmitter having:

an optical device formed of at least a first focus portion having afirst focal length, and a second focus portion having a second focallength at least longer than the first focal length; and

a light source provided in a position at a distance equal to or shorterthan the first focal length from the optical device, the light sourceemitting light to the optical device so that light travels to theoutside through the first focus portion and the second focus portion.

In the above-described arrangement, the optical device provided in thelight transmitter is formed of at least the first focus portion and thesecond focus portion, and the light source provided in the lighttransmitter is provided in a position at a distance equal to or shorterthan the first focal length from the optical device, and emits light tothe optical device so that light travels to the outside through thefirst focus portion and the second focus portion.

Accordingly, light emerging from the first focus portion in the lightemitted from the light source to the optical device has a smallexpansion angle such as not to diffuse largely and, therefore, can becaused to reach a long distance. On the other hand, light emerging fromthe second focus portion has a large expansion angle such as to diffuseto some extent and, therefore, can be caused to travel over ashort-distance area and, more particularly, over an area extended in awidthwise direction of a road surface.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configurational diagram showing a first embodiment of thepresent invention, FIG. 2 is a conceptional configurational diagram forexplaining the relationship between a focal length and an emergenceangle of an ordinary convex lens, and FIG. 3 is a conceptionalconfigurational diagram for explaining focal lengths and emergenceangles of a double-focus lens 7 in the first embodiment.

FIG. 4 is a conceptional diagram conceptually showing an emergencepattern of light from the double-focus lens 7, FIG. 5 is aconfigurational diagram showing a second embodiment of the presentinvention, FIG. 6 is a configurational diagram showing a thirdembodiment of the present invention, FIGS. 7A and 7B are configurationaldiagrams showing the configuration of a conventional art, and FIG. 8 isa configurational diagram showing the configuration of anotherconventional art.

FIG. 9 is a configurational diagram showing the configuration of amultiple focus lens 40 in a fourth embodiment of the present invention,FIGS. 10A and 10B are characteristic diagrams showing characteristics ofa semiconductor laser diode for use in the fourth and fifth embodimentsof the present invention, and FIG. 11 is a configurational diagramconceptually showing an emergence pattern of light from the multiplefocus lens 40 in the fourth embodiment.

FIGS. 12A, 12B, 12C are schematic configurational diagrams schematicallyshowing a multiple focus lens 53 in the fifth embodiment of the presentinvention, FIG. 13 is a conceptional diagram conceptually showing anemergence pattern of light from the multiple focus lens 53 in the fifthembodiment, and FIG. 14 is a conceptional diagram conceptually showingan emergence pattern of light from a lens in a fifth embodiment of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described below with respect toembodiments illustrated in the drawings.

FIG. 1 is a configurational diagram showing a first embodiment of thepresent invention.

Referring to FIG. 1, a light transmitter 5 formed of a box-like memberis constituted by a light source 6 which emits pulse-like light by adrive pulse signal and which is formed of a semiconductor laser diodefixed on the light transmitter 5, a double-focus lens 7 (correspondingto an optical device) integrally formed of glass, plastic or the like insuch a manner that a short-focus potion 7a (corresponding to a firstfocus portion) is placed about its center and a long-focus portion 7bl(corresponding to a second focus portion), and a photodiode 11 withwhich a light emitting state of the light source 6 is monitored.

Specifically, the light source 6 is disposed at a distance slightlysmaller than the focal length of the short-focus portion 7a of thedouble-focus lens such that light is emitted through the short-focusportion 7a at a narrow-expansion angle θa while light is emitted throughthe long-focus portion 7b at a wide expansion angle θb, thereby enablingthe light emitted through the short-focus portion 7a to cover along-distance area and the light emitted through the long-focus portion7b to cover a short-distance area which is an area extended to the leftand light (i.e., a widthwise direction of a road surface). Details ofthe double-focus lens will be described later.

On the other hand, a light receiver 8 formed of a box-like member isconstituted by an optical system 10 which condenses light reflected by areflex reflector or the like of a vehicle in front, and a photodiode 9which receives condensed light (pulse-like light) and whichphotoelectrically converts the received light.

A control circuit 1 is constituted by a pulse generator 2 whichgenerates a drive pulse signal to the light source 6, a pulse detector 3which detects a pulse signal from the photo diode 9, and a signalprocessing circuit 4 in which a transmission delay time from a lightemission start to a light receiving detection is obtained from anemission start signal from the pulse generator 2 (or a monitor signal(pulse signal) from the photo diode 11) and a light receiving detectionsignal from the pulse detector 3, and in which the distance to thereflector (vehicle in front) is measured on the basis of thistransmission delay time. In the signal processing circuit 4, aconfirmation is also made as to whether the light source 6 is suitablyemitting light on the basis of the monitor signal from the photodiode11.

The operation of the above-described arrangement will now be described.

When a drive pulse signal is generated from the pulse generator 2, thelight source 6 emits pulse-like light to the double-focus lens 7. Fromthe double-focus lens 7, the light emitted from the light source 6 isemitted at the narrow-expansion angle θa by the short-focus portion 7aand at the wide-expansion angle θb by the long-focus portion 7b. At thistime, the light emitting state of the light source 6 is monitored withthe photodiode 11, and an emission start signal corresponding to thestart of emitting light is output from the pulse generator 2 to thesignal processing circuit 4.

If part of the light emitted from the light transmitter 5 is reflectedby a reflex reflector or the like of a vehicle in front, it is condensedon the photodiode 9 by the optical system 10, and a pulse signal isgenerated by photoelectric conversion in the photodiode 9. The generatedpulse signal is immediately detected by the pulse detector 3, and areceiving detection signal corresponding to the received light detectionis output to the signal processing circuit 4.

Then, in the signal processing circuit 4, a transmission delay time fromthe light emission start to the light receiving detection is obtainedfrom the emission start signal from the pulse generator 2 (or themonitor signal (pulse signal) from the photodiode 11) and the lightreceiving detection signal from the pulse detector 3, and the distanceto the reflector (vehicle in front) is measured on the basis of thistransmission delay time. The result of this measurement is output asdistance information to an unillustrated display unit or the like to bedisplayed.

The relationship between the focal lengths and emergence angles of thedouble-focus lens 7 will next be described.

FIG. 2 is a conceptional configurational diagram for explaining therelationship between a focal length and an emergence angle of anordinary convex lens. Referring to FIG. 2, a condenser lens such as aconvex lens 36 has a characteristic such that if a point light source isplaced at a point A which is located at a distance corresponding to afocal length f from the center of the convex lens 36, light 100 from thepoint A becomes parallel light 110 by passing through the convex lens36.

On the other hand, if the point light source is placed at a point Bwhich is located at a distance f' shorter than the focal length f fromthe center of the convex lens 36, light 120 traveling from the point Band passing through the convex lens 36 emerges from the convex lens 36as light 130 having an expansion angle θ1 proportional to a distanceratio f'/f. Further, if the point light source is placed at a point Cwhich is located at a distance f" longer than the focal length f fromthe center of the convex lens 36, light 140 traveling from the point Cand passing through the convex lens 36 emerges from the convex lens 36as light 150 having a convergence angle θ2 proportional to a distanceratio f"/f.

From this general characteristic, the relationship between the focallengths of and emergence angles of the above-mentioned double focus lens7 is considered to be as shown in FIG. 3, which is a conceptionalconfigurational diagram for explaining the relationship between thefocal lengths of and emergence angles of the above-mentioned doublefocus lens 7.

Referring to FIG. 3, the above-mentioned light source 6 is placed at apoint E which is shifted a distance d toward the center of thedouble-focus lens 7 from a point D which is at a distance D' from thelens center corresponding to the focal length D of the short-focusportion 7a. Then, with respect to light 200 and 230 emerging from thelight source 6, light 200 emitted from the light source 6 emerges at anexpansion angle of θa/2 from parallel light 220 which is obtained whenthe light source 6 is placed at the point D. On the other hand, light230 emerges at an expansion angle θb/2 (θa<θb) from parallel light 250which is obtained when the light source 6 is placed in an unillustratedposition at a distance corresponding to the focal length of thelong-focus portion 7b from the center of the double-focus lens 7.

Accordingly, light 210 emerging from the short-focus portion 7a has asmall emergence angle (i.e., expansion angle) such as not to diffuselargely. Therefore, the emerging light can be caused to reach a longdistance. On the other hand, light 240 emerging from the long-focusportion 7b has a large emergence angle such as to diffuse to someextent. Therefore, the emerging light can be caused to travel over ashort-distance area and, more particularly, over an area extended in awidthwise direction of a road surface.

Next, an emergence pattern of light from the above-describeddouble-focus lens 7 will be described with reference to the conceptionaldiagram of FIG. 4, in which the coordinate represents detection distanceL (m) from the light transmitter 5 while the abscissa representsdetection width W (m), and in which broken lines designate an emergencepattern of light in the case of using the above-mentioned convex lens 36(FIG. 2).

As shown in FIG. 4, light emerging from the short-focus portion 7acovers the short-distance area with the expansion angle θa/2 from acenter, while light emerging from the long-focus portion covers along-distance area with the expansion angle θb/2 from the center.

As shown in FIG. 4, the detection distance changes with a change in theemergence angle depending upon the ratio of the areas of the short-focusportion 7a and the long-focus portion 7b as well as the factor based onthe above-described emergence angle. That is, the intensity of lightemerging from each of the short-focus portion 7a and the long-focusportion 7b is proportional to the glass area. Therefore, a farthestdetection distance and a nearest detection distance can be set bysetting the area ratio of the glass area of the short-focus portion 7aand the glass area of the long-focus portion 7b.

In the first embodiment of the present invention, as described above,two detection areas, i.e., a long-distance area and a short-distancearea can be provided without suitably moving the light source 6.Therefore, the detection range is not set one-sidedly and there is noneed to provide a drive circuit for moving the light source.

Also, the double-focus lens 7 formed of the short-focus portion 7a andthe long-focus portion 7b is used to diffuse light emitted from thelight source 6 to different extents (an extent such that diffused lightcloser to parallel light and a larger extent of diffusion). It isthereby possible to extend the detection width of the short-distancearea without sacrificing the maximum detection distance to realize adetection area suitable for an inter-vehicle control or obstacledetection apparatus.

In the above-described first embodiment, an emergence pattern of lightfrom the double-focus lens 7, such as that shown in FIG. 4, isillustrated. However, any other desired emergence pattern can be formedby independently changing the focal lengths of the short-focus portion7a and the long-focus portion 7b forming the double-focus lens 7, thedistance between the double-focus lens 7 and the light source 6, and theratio of the areas of the short-focus portion 7a and the long-focusportion 7b of the double-focus lens 7.

The optical system of the light transmitting section may be formed ofany multiple focus system other than the double-focus lens according toone's need. Further, the light transmitter 5 and the light receiver 8may be arranged integrally with each other (by combining the twobox-like units into one unit), although they are separately arranged inthe above-described first embodiment. The same can also be said withrespect to second to sixth embodiments described below.

The second embodiment of the present invention will be described withreference to FIG. 5. In the second embodiment, a transmission typehologram 18 is used as an optical system for a light transmitter insteadof the double-focus lens 7 of the first embodiment. A control circuit12, a pulse generator 13, a signal processing circuit 14, a pulsedetector 15, a light transmitter 16, a light source 17, a light receiver19, a photodiode 20, an optical system 21, and a photodiode 22 are thesame as the corresponding components of the first embodiment and,therefore, will not be explained.

Referring to FIG. 5, the transmission type hologram 18 of thisembodiment (corresponding to the optical device) can distribute, forexample, light having a small distortion in light waveform at anemission center of the light source to a short focus and a long focus atany ratio (evenly in some case) because the transmission type hologram18 can be manufactured as a transmission type hologram 18 having a shortfocus and a long focus existing mixedly by multiple exposure, while inthe case of the double-focus lens 7 of the first embodiment there is aneed to divide the internal region of the lens into the short-focusportion 7a and the long-focus portion 7b. Therefore, it is possible toeasily control a dispersion of the distance measuring accuracy withrespect to an area covered by the short-focus portion (long-distancearea) and an area covered by the long-focus portion.

Next, the third embodiment of the present invention will be describedwith reference to FIG. 6. In the third embodiment, a reflection typehologram 31 is used as an optical system for a light transmitter insteadof the double-focus lens 7 of the first embodiment. A control circuit23, a pulse generator 24, a signal processing circuit 25, a pulsedetector 26, a light transmitter 27, a light source 28, a light receiver32, a photodiode 33, an optical system 34, and a photodiode 35 are thesame as the corresponding components of the first embodiment and,therefore, will not be explained.

Referring to FIG. 6, the reflection type hologram 31 (corresponding tothe optical device) can be manufactured as a hologram having a shortfocus and a long focus existing mixedly by multiple exposure, as in thecase of the above-described second embodiment. Accordingly, the angle ofincidence upon the reflection type hologram 31 is set according to theplacement relationship between mirrors 29 and 30 and the light source 28by considering the reflection angle of the reflection type hologram 31.It is not necessary to use the mirrors 29 and 30 if the angle ofincidence upon the reflection type hologram 31 can be set only by theplacement of the light source 28 alone.

Next, the fourth embodiment of the present invention will be describedwith reference to FIG. 9. In the fourth embodiment, as shown in FIG. 9,a multiple focus lens 40 having a shape different from that of thedouble-focus lens 7 of the first embodiment is used. This multiple focuslens 40 has a cylindrical surface 40a for causing an emergence of lightat the expansion angle θa for a long-distance area (FIG. 1) and a flatsurface 40b for causing an emergence of light at the expansion angle θbfor a short-distance area (FIG. 1).

Referring to FIG. 9, the multiple focus lens 40 is formed of thecylindrical surface 40a having a predetermined radius of curvature, theflat surface 40b and an aspherical surface 40c. The cylindrical surface40a actually has a radius of curvature much larger than the radius ofcurvature of the aspherical surface 40c.

In the fourth embodiment, by the above-described arrangement, thecylindrical surface 40a and the aspherical surface 40c cause anemergence of light at the expansion angle θa for a long-distance area(FIG. 1), while the flat surface 40b and the aspherical surface 40ccause an emergence of light at the expansion angle θb for ashort-distance area (FIG. 1).

An example of the arrangement shown in FIG. 9 will be described below inwhich an outside shape G of the multiple focus lens 40 is φ30, theradius of curvature of the cylindrical surface 40a is R=135, the width Iof the cylindrical surface 40a is 15.5 mm, the radius of curvature ofthe aspherical surface 40c calculated by substituting R₀ =16 and K=-0.52in an equation shown below is Z, the thickness J of the multiple focuslens 40 is 10 mm, and a semiconductor laser diode 41 having itsdirectionalities shown in FIGS. 10A and 10B is disposed at a position ofL=20 mm on the optical axis of the cylindrical surface 40a. Thesemiconductor laser diode 41 is disposed so that the directionalityshown in FIG. 10A is parallel to the R direction of the cylindricalsurface 40a.

    Z=ch.sup.2 /[1+{1-(K+1)c.sup.2 h.sup.2 }.sup.1/2 ]+Ah.sup.4(1)

    (h.sup.2 =x.sup.2 +y.sup.2 c=1/R.sub.0)

In the optical radar apparatus set and arranged as described above,light is emitted by the semiconductor laser diode 41 in an emergencepattern such as that shown in FIG. 11. At this time, the expansion angleθa for a long-distance area is 2.96° while the expansion angle θb for ashort-distance area is 9.8°.

An example of a modification of this embodiment may be such that, in themultiple focus lens 40 shown in FIG. 9, a diffusing flat surface plate(corresponding to the diffusing flat surface portion), for example, isused in place of the flat surface 40b, and this diffusing flat surfaceplate 40b and a spherical lens having the cylindrical surface 40a or thelike (corresponding to the focus portion) are combined. In this case,however, light emerges only from the flat surface 40b, i.e., thediffusing flat surface plate for the short-distance area. Therefore, thelight is diffused and weakened by the diffusing flat surface plate,thereby slightly reducing the detection distance.

Next, the fifth embodiment of the present invention will be describedwith reference to FIGS. 12A to 12C. In the fifth embodiment, as shown inFIG. 12C, light sources 52 formed of three arrays of semiconductor laserdiodes 51 are used along with a multiple focus lens combining anaspherical surface to form an emergence pattern of light by three beams.FIG. 12B is a cross-sectional view taken along the line B--B of FIG.12A, and FIG. 12C is a cross-sectional view taken along the line A--A ofFIG. 12A.

The multiple focus lens 53 is formed by, as viewed in thecross-sectional view shown in FIG. 12B, a spherical surface 53b having apredetermined curvature and an aspherical surface 53a having a curvaturecalculated by an equation 2 shown below, and is formed by, as viewed inthe cross-sectional view shown in FIG. 12C, a spherical surface 53dhaving a predetermined curvature and an aspherical surface 53c having acurvature calculated by an equation 3 shown below.

    X=c.sub.0 Y.sup.2 /[1+{1-c.sub.0.sup.2 Y.sup.2 }.sup.1/2 ]-ΣA.sub.i |Y|.sup.i                               (2)

    X=c.sub.0 Z.sup.2 /[1+{1-c.sub.0.sup.2 Z.sup.2 }.sup.1/2 ]-ΣA.sub.i |Z|.sup.i                               (3)

In the case of using the multiple focus lens 53 having differentcurvatures at different viewing angles along with light sources 52formed of three arrays of semiconductor laser diodes 51 as mentionedabove, a resulting emergence pattern of light has a three-beamconfiguration as shown in FIG. 13.

In this case, if the distance dd between laser chips of the three arraysis set to 0.5 mm and if the light sources 52 are disposed so that thedirectionality of FIG. 13B is parallel to the plane of paper, then anexpansion angle θc for a long-distance area of one beam is 1°, anexpansion angle θe between the beam optical axes is 1°, and an expansionangle θd for a short-distance area of the three beams as a whole is 10°.In this embodiment, the number of beams, which is three in thisembodiments, may be any number while the same design is adopted.

Next, the sixth embodiment of the present invention will be described.With respect to the first to fifth embodiments, only expansion of lightin the horizontal direction was described. However, expansion of lightin a vertical direction may be taken into consideration, for example, bychanging the spherical surface 53b of the multiple focus lens 53 of thefifth embodiment into an aspherical surface at least having a curvaturecalculated by the equation 2. For example, in such a case, an emergencepattern of light such as the pattern shown in FIG. 13 is exhibited inthe horizontal direction, while a pattern such as that shown in FIG. 14is exhibited in the vertical direction.

If an expansion in a vertical direction is provided in this manner, itis specifically preferable to set the light transmitter and lightreceiver portions of the optical radar apparatus on a rearview mirrorportion in a vehicle passenger chamber.

That is, in a case where an expansion in a vertical direction is to beprovided, there is a need to prevent the bonnet of a vehicle using theapparatus from reflecting light and stopping the light from traveling inthe desired direction, and setting in an upper position is thereforepreferred. In the case of setting outside the vehicle, however, thedetection accuracy may be reduced by occurrence of a dust contaminationor the like upon light transmitting, receiving or the like.

Then, the light transmitter and light receiver portions of the opticalradar apparatus are disposed not only in the vehicle passengercompartment but also in the range of wiping of a windshield wiper forremoving a contamination on a windshield, thereby enabling thewindshield wiper to remove a contamination on the windshield in front ofthe light transmitter and light receiver portions of the optical radarapparatus. The detection accuracy can be thereby maintained as high aspossible.

The present invention is not limited to the above-described embodimentsand can be practiced in various forms in a scope such as not to departfrom the gist of the invention.

INDUSTRIAL APPLICABILITY

In the present invention, as described above, a long-distance area and ashort-distance area can be simultaneously set as detection rangesaccording to the optical device, the light source and the placementrelationship between the optical device and the light source. It istherefore possible to increase the expansion angle in a road surfacedirection in the short-distance area without setting the detectionranges one-sidedly and without sacrificing the maximum detectiondistance. Specifically, if the present invention is applied to a radarapparatus for use with a constant-speed traveling apparatus mounted on avehicle, the expansion angle in a road surface direction in theshort-distance area can be increased without setting the detectionranges one-sidedly and without sacrificing the maximum detectiondistance. It is thereby possible to accurately detecting obstaclesexisting in the vicinity of the vehicle while maintaining a suitabledistance between the vehicle and another vehicle.

What is claimed is:
 1. An optical radar apparatus for a vehicle having alight transmitter for emitting a beam of light, from a front side ofsaid vehicle toward an object, a light receiver for receiving reflectedlight from said object, and distance calculating means for calculating adistance to said object based on said beam of light and said reflectedlight, said light transmitter comprising:an optical device including ann-focus lens (n is equal to or greater than 2) formed of at least afirst focus portion having a first focal length and a second focusportion, first and second parts of which are respectively disposed onopposite sides of said first focus portion, said second focus portionhaving a second focal length longer than the first focal length, saidfirst and second focus portions being disposed in an order of said firstpart of said second focus portion, said first focus portion, and saidsecond part of said second focus portion, and disposed in one of a widthand a height direction of said vehicle, from an edge of said n-focuslens to an opposite edge of said n-focus lens; and a light sourceprovided in a position at a distance equal to or shorter than the firstfocal length from said optical device, said light source emitting lightto said optical device so that light is emitted toward said front sideof said vehicle through said first focus portion and said second focusportion.
 2. An optical radar apparatus for a vehicle according to claim1, wherein said optical device is formed of a hologram.
 3. An opticalradar apparatus for a vehicle according to claim 1, wherein said opticaldevice has:a cylindrical surface having a predetermined focal length,said cylindrical surface being disposed at a side of said optical devicewhere light from said light source enters said optical device; a flatsurface disposed adjacent to said cylindrical surface at said side ofsaid optical device where light from said light source enters saidoptical device; and an aspherical surface disposed on a side of saidoptical device other than said side where light from said light sourceenters said optical device; said first focus portion being formed bysaid cylindrical surface and said aspherical surface, said second focusportion being formed by said flat surface and said aspherical surface.4. An optical radar apparatus for a vehicle having a light transmitterfor emitting a beam of light from a front side of said vehicle toward anobject, a light receiver for receiving reflected light from said object,and distance calculating means for calculating a distance to said objectbased on said beam of light and said reflected light, said lighttransmitter comprising:an optical device formed of at least a focusportion having a predetermined focal length, and a diffusing flatsurface portion disposed adjacent to said focus portion; and a lightsource provided in a position at a distance equal to or shorter than thepredetermined focal length from said optical device, said light sourceemitting light to said optical device so that light travels to outwardlythrough said focus portion and said diffusing flat surface portion. 5.An optical radar system comprising:a light source; a lens for focusinglight from said light source, said lens having a first portion having afirst focal length and a second portion having a second focal lengthdifferent from said first focal length; a receiver for generating anelectrical signal representative of reflected light from said lightsource, said reflected light from said light source being focused bysaid lens; and distance calculating means, operatively connected to saidlight source and said receiver, for calculating a distance of areflection point of said reflected light; wherein said lens has adiffusing surface.
 6. The optical radar system of claim 5, wherein saidlens has a cylindrical surface.
 7. A mobile optical radar unitcomprising:an automobile; and an optical radar system mounted in saidautomobile, said optical radar system includinga light source, a lensfor focusing light from said light source and projecting said focusedlight to an exterior of said automobile, said lens having a firstportion having a first focal length and a second portion having a secondfocal length different from said first focal length, a receiver forgenerating an electrical signal representative of light reflected tosaid automobile from said light source, said light reflected to saidautomobile from said light source being focused by said lens, anddistance calculating means, operatively connected to said light sourceand said receiver, for calculating a distance of a reflection point ofsaid reflected light from said automobile; wherein said lens has adiffusing surface.
 8. The mobile optical radar unit of claim 7, whereinsaid lens has a cylindrical surface.